Assessing Pesticide Occurrence and Burrowing Mayfly Declines in the Upper Mississippi River

Burrowing mayflies are a key water quality indicator on the Mississippi River, supplying trillions of calories to fish, birds, and other wildlife. Recent observations (weather radar, benthic invertebrate surveys, public reports) are showing substantial mayfly population decline over the past 15–20 years, coinciding with shifts in river flow, habitat, and pesticide use. Recent Wisconsin water samples frequently exceed acute and chronic benchmarks for the neonicotinoids clothianidin and imidacloprid and contain complex mixtures of pesticides. Sediment sampling also reveals diverse pesticide mixtures and elevated concentrations of the synthetic pyrethroid bifenthrin, with some Mississippi River sediments exceeding 10-day lethal concentration benchmarks for lab organisms. Mayfly tissues now contain similar pesticide mixtures. The Upper Mississippi River Conservation Committee recently listed imidacloprid, clothianidin, thiamethoxam, and bifenthrin among its top contaminants of concern.

Shawn Giblin is the Mississippi River Water Quality Specialist for the Wisconsin Department of Natural Resources. A Brice Prairie native, he developed a deep connection to the Mississippi River through early years spent hunting, fishing, hiking, boating, camping, and canoeing on the river. Before joining the Wisconsin DNR in 2006, Shawn worked with the University of Wisconsin–Center for Limnology, the U.S. Fish and Wildlife Service, and Colorado State University’s Center for Environmental Management of Military Lands. His research focuses on channel connectivity and its influence on water quality, drivers of water clarity, ecological thresholds affecting free-floating plants and algae, interactions among water quality, fish and wildlife populations, pesticides and emerging contaminants, and climate change adaptation.

Shawn lives in rural West Salem with his family. When he’s not in the field, he enjoys hunting, fishing, cross-country skiing, camping, and canoeing.